Flat display technology has been significantly advanced recently, in part because manufacturing thin film transistors on a substrate such as glass has become a mature skill. This facilitates the development of active matrix type display devices. In addition to liquid crystal materials, which need a backlight when used for flat displays, an electro-luminescent device, such as an organic light emitting diode (OLED), which can emit light itself, is actively researched. The feature of self-light-emission is one of the reasons that the display comprising electro-luminescent devices is brighter than a backlit liquid crystal display.
FIG. 1 is a schematic diagram of a conventional electro-luminescent display panel using OLEDs. The OLED panel comprises a data driving circuit, a scan driving circuit, a plurality of scanning lines G1 and G2, a plurality of data lines D1-D6 crossing the scanning lines to form a plurality of pixel regions P1-P12, a plurality of switching thin-film-transistors (TFT) S1-S12, a plurality of pixel driving TFT T1-T12, and a plurality of OLEDs R1, G1, B1 through R4, G4, B4. OLEDs R1, R2, R3, and R4 emit red light. OLEDs G1, G2, G3, and G4 emit green light. OLEDs B1, B2, B3, and B4 emit blue light.
Each pixel region P1-P12 comprises a TFT area and an OLED area. The TFT area includes a switching TFT and a pixel driving TFT. Conventionally, all OLED areas have the same structure regardless of the color of light emitted by OLEDs. FIG. 2 shows the structure of an OLED area. An OLED 290 is disposed above an intermediate structure 250 which is disposed above a substrate 200. The OLED 290 comprises at least an anode, such as an indium tin oxide (ITO) layer 260, an organic light emitting layer 270, and a cathode layer 280. The intermediate structure 250 includes a passivation layer 240, an interlayer dielectric (ILD) 230, a gate oxide layer 220, a silicon oxide layer (SiOx) 215, and a silicon nitride layer (SiNx) 210.
When a current is applied to the ITO (anode) layer 260 and the cathode layer 280, light emitted from the organic light emitting layer 270 is transmitted toward the bottom direction through the ITO layer 260, the intermediate structure 250 and the substrate 200. However, the intermediate structure 250 has different optical effects (such as absorption, transmission, and reflection) on light of different colors including red, green, and blue. Therefore, a specific same intermediate structure may have a better optical effect on blue light that on red light and/or green light. As a result, the color saturation and transmission rate of an OLED panel is not optimized.